Free radicals cyano groups

Various transition metals have been used in redox processes. For example, tandem sequences of cyclization have been initiated from malonate enolates by electron-transfer-induced oxidation with ferricenium ion Cp2pe+ (51) followed by cyclization and either radical or cationic termination (Scheme 41). ° Titanium, in the form of Cp2TiPh, has been used to initiate reductive radical cyclizations to give y- and 5-cyano esters in a 5- or 6-exo manner, respectively (Scheme 42). The Ti(III) reagent coordinates both to the C=0 and CN groups and cyclization proceeds irreversibly without formation of iminyl radical intermediates.The oxidation of benzylic and allylic alcohols in a two-phase system in the presence of r-butyl hydroperoxide, a copper catalyst, and a phase-transfer catalyst has been examined. The reactions were shown to proceed via a heterolytic mechanism however, the oxidations of related active methylene compounds (without the alcohol functionality) were determined to be free-radical processes. 

In this system a very stable dimeric species is formed via reaction of a second nickel(I) species complexing to the cyano group. Of interest is the fact that the cyclization rate Aec is 4 orders of magnitude slower than that for the free radical alone. 

However, it has already been demonstrated that other unsaturated groups (alkynes and cyano) as well as olefins in a nonterminal position can undergo hydrosilation on a silica hydride surface [25,26]. The cyano group is amenable to hydrosilation only in the absence of an olefin and with a free radical initiator as the catalyst giving two possible products as shown below [27]. 

Radical anions of geminal nitro compounds in DMF cleave rapidly to nitrite and a radical which initiate a free radical chain in which a v/c-dinitro compound is formed [43]. Radical anions of other a-substituted nitroalkanes may cleave either the nitro group or the other substituent 1-cyano-l-nitrocyclohexane thus splits off nitrite whereas 1-nitrocyclo-hexyl p-tolyl sulfone loses p-tolylsulfinate [44]. 

Diazotization of a-aminonitriles has been reported to generate free radicals, presumably from the diazonium ion. The cyanide group is clearly important, as this reaction is usually observed only with cyano diazonium ions. Diazotization of 2-amino-2-methylpropanenitrile (179) yields 2-nitrosopropanenitrile (180) which can be trapped to give 181, presumably by reaction of the radical 182 with NO. Further evidence of the existance of 182 is provided by observation of its dimerization product. 

The types of compounds that can be polymerized readily by the radical-chain mechanism are the same types that easily undergo free-radical addition reactions. Alkenes with aryl, ester, nitrile, or halide substituent groups that can stabilize the intermediate radical are most susceptible to radical polymerization. Terminal alkenes are generally more reactive toward radical-chain polymerization than more highly substituted isomers. The dominant mode of addition in radical-chain polymerization is head-to-tail. The reason for this orientation is that each successive addition of monomer takes place in such a way that the most stable possible radical intermediate is formed. For example, the addition to styrene occurs to give the phenyl-substituted radical to acrylonitrile, to give the cyano-substituted radical ... 

Terpolymers of tetrafluoroethylene, perfluoromethyl vinyl ether, and small amounts of a cross-linking termonomer, such as, for example, perfluoro(4-cyanobutyl vinyl ether), are free radically copolymerized in emulsion. Vulcanization occurs by cyclotrimerization of the cyano groups to s-triazine rings. The elastomer has a glass transition temperature of —12 C and a brittle temperature of —39° C. It is very resistant to weathering and possesses a good low-temperature flexibility. 

In conclusion, free radical intramolecular addition to the cyano group, although not much studied, is a facile process. In all the cases reported, addi-... 

More recently, the controlled radical polymerization (CRP) by various methods including atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization, and nitroxide-mediated polymerization (NMP), as well as cyano q l-mediated free radical polymerization have allowed chemists to synthesize well-defined glycopolymers that, in some cases, have particular end-group functionalities. A review focuses on the synthesis of original glycopolymers by these techniques and their applications. ... 

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